Establishment and verification of a method for analyzing nasal blackheads images

Abstract Background As people pay more attention to their skin health and the demand of developing skin care products for facial blackheads grows, the value of objective and efficient image recognition methods for blackheads is becoming more evident. Inspired by this current situation, this study attempted to analyze the number of blackheads of different severity automatically on the nose using an object recognition method on photographs of the nasal blackheads of subjects. Method This study collected 350 subjects’ facial photos in the laboratory environment, who aged 18–60, with blackhead symptoms in the nasal region. And expert assessment was used as a reference for machine learning to verify the performance of the nasal blackhead image recognition model through consistency and correlation analysis. Results The study concluded that the algorithm accuracy reached above 0.9, the model itself was effective, and the consistency between the model and the expert assessor assessment results was good, with the number of nasal blackheads, the count of blackheads of different severity, and the intra‐group correlation coefficient ICC of blackhead severity all above 0.9, indicating that the deep learning‐based assessment model had high overall performance and the evaluation results were comparable to those of the expert assessor. Conclusion The recognition and analyzing model of nasal blackhead images provides a scientifically objective and accurate method for identifying the number and evaluating the severity of nasal blackheads. By using this model, the efficiency of evaluating nasal blackhead images in the cosmetics clinical trial will be improved. The assessment result of nasal blackheads will be objective and stable, and not only rely on the professional knowledge and clinical experience of assessors. The model can try to be applied in cosmetics efficacy testing and continuously optimized.


INTRODUCTION
Blackheads, also known as blackheads, are a non-inflammatory, mild type of acne that is caused by clogged hair follicles due to dead cells in the pores and skin oils.Blackheads usually occur on the face, especially on the nose, but they also appear on the back, chest, neck, arms, and shoulders.It is characterized by dark spots in visibly enlarged pores that are squeezed into the shape of worms with black tips. 1 As people pay more attention to their skin health, more and more consumers need to improve their facial blackheads through modern medical measures or skin care measures.Overall, the latter class of methods is more refined in its recognition and more demanding.
In this study, the object recognition method in the neural network approach is used to train the model to learn the data from the expert assessor's evaluation of the images, output the severity classification of individual blackheads, and then obtain the number of blackheads with different severity levels and the overall blackhead severity, respectively.

Subjects
The sample for this study was 350 healthy Chinese men and women in the age range of 18−60 years.The primary inclusion criteria were sub-jects without facial skin conditions such as dermatitis and subjects with symptoms of blackheads in the nasal region.The study was conducted from May 2020 to February 2021.

Experimental methods
Subjects followed their daily skincare routine, signed an informed consent form, and completed a medical history survey at first visit.
After formal enrollment, the face was cleansed with a standard daily cleanser and balanced for 30 min (20 • C−24 • C, 40%−60% room humidity).After confirmation of final enrollment conditions, a full-face photograph of the face was completed.

Algorithm flow chart
A flow chart of image acquisition and blackhead identifying algorithm establishment is shown in Figure 1.
F I G U R E 1 Schematic diagram of the input and output of the nasal blackhead identification and index calculation system.
TA B L E 1 Severity grade of blackheads on the nose.

Description of Clinical symptom Mild Moderate Severe
Oxidized gray acne, showing finer acne: smaller area and less severe symptoms.
Oxidized gray acne, showing as more pronounced acne: larger area, moderate symptoms.
Completely oxidized, deep black blackheads: the largest areas and most pronounced symptoms.
F I G U R E 2 Schematic diagram of the data annotation process for the nasal blackhead symptom model.

Image acquisition
After face cleansing and balancing for 30 min, subjects took facial photo through the VISIA-CR device to capture left-sided, right-sided, and frontal facial images.

Visual perception assessment
A face recognition technology was used to locate the nose tip area of the face images and crop it to a fixed size (640*640) to form a base image library for data annotation.Then two expert evaluators labeled these nasal images for blackhead symptoms and blackhead severity grade, by the open-source annotation program Ybat (YOLO BBox Annotation Tool). 4 The blackhead assessment standard is shown in Table 1.* The expert evaluator marked the blackheads on the nasal image, and blue box is for mild severity level of blackhead, green box is for moderate one, orange box is for severe one, as shown as in

Image processing
The model is trained using the YOLO-v5 which is a target detection

F I G U R E 5
Graph of average precision, accuracy, and recall.mAP was used to measure the accuracy of blackheads recognition algorithms.Precision and recall were used to measure the accuracy of blackheads severity level algorithms.

Statistical methods
SPSS 24.0 software was used for the statistical analysis of the data.
Correlation between image analysis and expert assessor visual perception assessment: Pearson; consistency between two expert assessors for visual perception assessment; consistency between image analysis and expert assessor for visual perception assessment: intragroup correlation coefficient ICC.ICC should be greater than 0.80; 0.61-0.80 is moderate; 0.41-0.60 is fair; 0.11-0.40 is low; and below 0.1 there is no consistency. 8

Consistency analysis of the two expert assessors' visual perception assessment
The results of the agreement analysis between the two expert assessors' visual perception assessment are shown in

Consistency analysis of the two image analyses
Two image analyses were performed on 350 VISIA-CR photographs by the nasal blackhead image recognition model, and the machine output was consistent.The intra-group correlation coefficients for both image analyses were 1.000 for the number of nasal blackheads, the number of mild blackheads, the number of moderate blackheads, the number of severe blackheads, and the severity of blackheads.

Correlation analysis of visual perception assessment and image analysis
The results of the correlation analysis between the expert assessor's visual perception assessment and image analysis are shown in Table 3.The Pearson correlation coefficients for the number of nasal blackheads, the number of mild blackheads, the number of moderate blackheads, the number of severe blackheads, and the severity of blackheads were all over 0.9 (p<0.05), with a high correlation.

Consistency analysis of visual perception assessment and image analysis
The results of the consistency analysis of the visual perception assessment and image analysis are shown in Table 4.The intra-group correlation coefficients for the number of nasal blackheads, the number of mild blackheads, the number of moderate blackheads, the number of severe blackheads, and the severity of blackheads exceeded 0.9 (p<0.05) with good consistency.

CONCLUSION
Consistency refers to the interchangeability of two measurement methods 9 or the equivalence of the results when applying the same As a quantitative evaluation method, the counting method seems to be a more objective grading method, but the method is more tedious and time-consuming.
In this study, the intra-group correlation coefficients (ICC) of the number of nasal blackheads, the count of blackheads of different sever- However, due to the limited time cost of this study, there are some shortcomings, such as the small sample size of the study sample, so the sample needs to be expanded in the future to further validate the performance of the model; another example is that this study only targets blackheads on the nose, and further research will be conducted on blackheads in other areas, and more methods are also expected to make effective and rapid determination of blackheads.
Blackhead identification and evaluation are widely used in clinical efficacy evaluation.Now the examination, counting, and evaluation of the severity of facial blackheads are mainly rely on the empirical judgment of a dermatology professional or expert assessor.The manual evaluation of facial blackheads is highly subjective and ambiguous, and the diagnosis results are closely related to the experience of the dermatology or expert assessor.The diagnosis of facial blackheads requires expertise in dermatology and much clinical experience, and the efficiency of manual evaluation is also relatively low, because it needs dermatology's or expert evaluator's person-by-person or photo-by-photo evaluation.Therefore, the traditional method of relying on the dermatology's or expert evaluator's clinical experience judgment is no longer able to meet the demand for accurate diagnosis of facial blackheads.At present, in addition to clinical assessment, there are two types of typical image recognition blackhead diagnosis methods.The first is through image conversion plus threshold segmentation, where the image can represent the characteristics of blackhead symptoms, using image processing to highlight; 2 the second is based on neural network model methods, 3 which is subdivided into two kinds, blackhead severity classification and blackhead symptoms point object recognition.The above two types of blackhead diagnosis methods have advantages and disadvantages, among which the first type, based on image conversion and threshold segmentation, has errors in recognition for different individuals and different severity levels; in the second type, based on training models and rank segmentation based on actual size and dimension, the representativeness of symptom levels has to be verified.

Figure 2 .
And the annotation file includes the horizontal coordinate x of the center point of the annotation box, the vertical coordinate y of the center point of the annotation box, the width w of the annotation box, and the height h of the annotation box.All images used in this study were privacy masked, and the training images were all intercepted perinasal images, which did not involve * Ybat is an open-source object detection dataset annotation tool that can continuously annotate and save in various required formats.any factors related to personal privacy identification.The blackhead dataset was divided into three separate subsets for training, validation, and testing.
model.Before formal model training, considering the model's generalization performance and the effective utilization and exploration of features in the base images, operations are performed on the images, including scaling, translation, cropping, rotation, color transformation, and other operations.Scaling involves resizing photos to different degrees to adapt to different distances or pixel resolutions in photo capture.Translation and rotation are done to enable the model to adapt to photos taken from different positions and angles.Cropping is used to make the model adaptable to different shooting backgrounds and occlusions.Color transformation involves applying various transformations to the image's hue, saturation, and brightness separately and in combination.The examples of image enhancement and transformation are as shown as in Figure 3.
Use YOLO-v5 for deep learning training and algorithm establishment on enhanced and transferred images.

F I G U R E 3
Example of image enhancement and transformation processing.The mAP metric is used in the study to measure the model's performance. 5mAP is the full name of mean average precision in English and is also an important metric for measuring the accuracy of the object detection algorithms in deep learning.The calculation of mAP involves IOU, TP, FP, FN, and other concepts.† mAP is maximum 1, minimum 0, the larger the value, the better; the curve of mAP and recall will keep rising with the training time, signifying the object detection rate keeps improving.IoU (Intersection over Union) is widely used in deep learning and measures the degree of overlap between the prediction box and the ground truth box in object detection, 6 and a parallel intersection ratio greater than 0.5 is considered as TP (True Positive) that is, correct matching and prediction.The image explanation about IOU is shown in Figure 4.The average precision, accuracy, and recall curves of the model are shown in Figure 5, and with the training time, the detection rate keeps improving, all close to 1. 7 The average precision for IoU of 0.5 † Mean average precision is calculated as: mAP = TP/(TP+FP).IOU (intersection-over-union) is the parallel intersection ratio.TP (True Positive) indicates that positive samples predicted by the model to be positive.FP (False Positive) indicates that negative samples predicted by the model to be positive.

F I G U R E 4
Image interpretation diagram of IOU. is 0.9975; the average precision on different IoU thresholds is 0.9646; the accuracy is 0.9934; and the recall is 0.9983.The model works well.‡ ‡ Recall is calculated as: Recall = TP/(TP+FN).
ity, and the severity of blackheads between different assessors were all above 0.8 and in good agreement.The consistency of the nasal blackhead image recognition model with the results of the expert assessor and the intra-group correlation coefficients (ICC) for the number of blackheads, the count of blackheads of different severity, and the severity of blackheads were above 0.9, indicating that the assessment model based on deep learning has a high overall performance and the evaluation results are comparable with those of the expert assessor.The nasal blackhead image recognition model provides a scientific, objective, and accurate method for identifying and evaluating the severity of nasal blackheads.The model provides objective and stable evaluation criteria for the diagnosis of nasal blackhead symptoms, avoids diagnostic errors caused by the subjectivity and ambiguity of different evaluators' judgments, and does not depend on the professional knowledge and clinical experience of the evaluator so that consumers can rely on the device to automatically complete the evaluation of nasal blackhead severity without a professional evaluator.In addition, the model has important practical significance by improving the efficiency of blackhead image evaluation.Follow-up studies will continue to validate the performance of this model with more data from additional cosmetic clinical trials.

TA B L E 2
Consistency analysis of the two expert assessors' visual perception assessment.Pearson correlation analysis of visual perception assessment and image analysis.
group correlation coefficients for the number of nasal blackheads, the number of mild blackheads, the number of moderate blackheads, the number of severe blackheads, and the severity of blackheads exceeded 0.8 (p<0.05) with good agreement.TA B L E 3